Commonly known as knotweed or polygonatum, Persicaria affinis are low growing, mat forming weed smotherers par excellence. 'Darjeeling Red' is a cultiver where the flowers open a very pale pink, which gradually darken to deep crimson as the season progresses. I've known it start flowering in May and still to be going in late October. Growing only 25cm high or so, it can spread quite widely, up to a metre or so, but is easy to keep in check if required. The semi evergreen leaves are narrow and mid green, streaked with crimson as the season advances, and often turning a bright crimson in autumn and early winter. Holds an RHS Award of Garden Merit, is extremely cold tolerant and will grow in most soils and conditions, except waterlogged deep shade, so a very useful and versatile plant indeed.